1. Field of the Invention
The present invention relates to a stacked type dielectric resonator which constitutes a resonance circuit in a microwave band in a range of several hundreds MHz to several GHz. In particular, the present invention relates to a stacked type dielectric resonator which has a compact size, which involves low loss, and which is usable, for example, for band-pass filters, duplexers, and oscillators.
2. Description of the Related Art
Recently, wireless communication systems such as portable telephones are diversified, it is strongly demanded for the stacked type dielectric filter to realize a compact size and low loss.
In order to realize the low loss of the stacked type dielectric filter, it is necessary to improve the no-load Q of a stacked type dielectric resonator which constitutes the stacked type dielectric filter. The no-load Q of the resonance circuit is principally determined by the loss (dielectric loss) due to the dielectric of the dielectric substrate and the loss (conductor loss) due to the stripline conductor. In general, in a low frequency band which is equivalent to or lower than the microwave band, the conductor loss is dominant for the no-load Q as compared with the dielectric loss.
Therefore, in order to realize the low loss of the stacked type dielectric filter and improve the no-load Q, the following means are conceived.
(1) The specific resistance of the conductor material for forming the stripline conductor is decreased.
(2) The width and the thickness of the stripline conductor are increased.
However, the means (1), in which the specific resistance is decreased as described above, causes such a fear that any limit may arise concerning the material and the cost. The means (2), in which the size of the stripline conductor is increased, causes such a problem that an electronic part including the stacked type dielectric resonator may become large.
In view of the above, for example, the following means has been hitherto suggested. That is, a pair of ground electrodes are formed on upper and lower surfaces of a dielectric substrate. A stripline conductor is stacked in parallel to the ground electrodes between the pair of ground electrodes with dielectric layers intervening therebetween (see Japanese Laid-Open Patent Publication No. 4-43703).
However, in this case, a concern arises such that the adjustment for the resonance frequency may involve a number of difficulties, because the short-circuited end of the stripline conductor is exposed to only the upper and lower surfaces of the dielectric substrate.
The present invention has been made taking the foregoing problems into consideration, an object of which is to provide a stacked type dielectric resonator which has a simple structure, which makes it possible to effectively reduce the conductor loss which would be otherwise caused by a stripline conductor, and which makes it possible to improve the no-load Q of the resonator.
Another object of the present invention is to provide a stacked type dielectric resonator which makes it possible to adjust the resonance frequency with ease, in addition to the requirement described above.
According to the present invention, there is provided a stacked type dielectric resonator comprising a dielectric substrate including a plurality of dielectric layers stacked and integrated into one unit; and a ground electrode and a stripline conductor stacked with each other with the dielectric layer interposed therebetween; wherein a first end of the stripline conductor is electrically connected to the ground electrode; and the stripline conductor is provided with an additional member for increasing a portion through which a high frequency current in a microwave band flows.
Accordingly, in the present invention, the portion, through which the high frequency current in the microwave band flows, is successfully increased by the aid of the additional member. Therefore, it is possible to effectively reduce, with the simple structure, the conductor loss which would be otherwise caused by the stripline conductor. Further, it is possible to improve the no-load Q of the resonator.
It is preferable that the additional member is composed of a via hole for electrically connecting the stripline conductor and the ground electrode. In this arrangement, it is preferable that the ground electrode is stacked with the dielectric layers intervening therebetween so that the stripline conductor is interposed therebetween; and the additional member is composed of via holes extending in both directions from the stripline conductor to portions of the ground electrode respectively. By doing so, the portion, through which the high frequency current in the microwave band flows, is further increased, and thus it is possible to further improve the no-load Q of the resonator.
Especially, when the via hole is formed at a position deviated toward the first end of the stripline conductor, the conductor loss, which may be caused by the stripline conductor, can be effectively reduced, while ensuring the electrical length of the stripline conductor.
When the first end of the stripline conductor is electrically connected to the ground electrode at the surface of the dielectric substrate, the first end of the stripline conductor is exposed from the dielectric substrate during the production process for the stacked type dielectric resonator. Therefore, it is easy to change the length of the stripline conductor, and thus it is easy to adjust the resonance frequency.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.